1. Field of the Invention
This invention relates to power transmission belts and, more particularly, to a power transmission belt having teeth spaced at regular intervals along the length of the belt. The invention is also directed to a method of making such a belt.
2. Background Art
Power transmission belts with drive teeth are used in many different environments. Belts of this type are also referred to as cogged belts and are used commonly as part of a gear shifting mechanism on a snowmobile or scooter, or in other general industrial applications.
In gear shifting mechanisms, these belts are wrapped around driving and driven pulleys. The pulleys are reconfigurable to vary their effective diameter, whereby speed changes can be effected. The belts used in this application are either single- or double-cogged in construction. That is, the belts have inside and outside surfaces with teeth/cogs on one or both of these surfaces. The teeth are spaced at regular intervals along the length off the belt body, with troughs defined between adjacent teeth. The belts of this type are normally made with compression and tension rubber layers between which a cushion rubber layer is provided and in which a load carrying member, such as an elongate cord, is embedded. Typically, the sides of the belts will not be covered by any type of fabric. This type of belt is referred to as a “raw edge” type belt.
There are a number of different methods by which belts of this type are made. In one form, a cylindrical shaping die/mold is used, upon which belt components are serially applied. In one exemplary belt construction, the first component placed upon the shaping die/mold is an outer reinforcing cloth layer, followed by a rubber sheet defining the tension rubber layer, a load carrying member/cord, a rubber sheet defining the compression rubber layer, and an inner reinforcing cloth layer. A cylindrical sleeve, having alternating protrusions and grooves around an inner circumferential surface thereon, is placed surroundingly over the components built up upon the shaping die/mold. Vulcanization is then carried out under controlled pressure and temperature conditions. During vulcanization, the inner reinforcing cloth layer is contracted to thereby emboss the rubber sheet defining the compression rubber layer. One problem with this type of construction is that the belts tend to expand. To avoid this problem, an alternative manufacturing method has been used.
In this alternative method, a rubber sheet/layer is placed against a planar shaping die/mold having alternating projections/recesses extending along the length thereof. The projections/recesses are complementary to the desired end shape of the teeth and troughs on the belt compression section. The shaping die/mold has a length greater than the length of the belt to be made. The rubber sheet/layer is pressed against the shaping die/mold under controlled temperature and pressure conditions to cause the sheet/layer to conform to the projections/recesses on the shaping die/mold. A resulting cog pad is then separated from the shaping die/mold and wrapped around a cylindrical die/mold having a peripheral surface with projections/recesses complementary to the teeth and troughs on the cog pad. The cog pad is wrapped into a continuous shape around the cylindrical die/mold and its complementarily-shaped ends butt joined. One or more load carrying members are then wrapped around the cog pad, followed successively by another rubber layer and a reinforcing cloth layer, to define a sleeve preform that is subsequently vulcanized. Further details of a process of this type are set forth in JP 2002-1691 A.
In yet another method of making belts of the above type, a cylindrical shaping die/mold is utilized. A reinforcing cloth layer and rubber sheet, defining a compression rubber layer, are wrapped around the shaping die/mold, that has projections/recesses that are complementary to the alternating teeth and troughs of a completed belt. After these two components are put in place, a jacket is placed surroundingly over the shaping die/mold. Thereafter, the compression rubber layer is pressed against the shaping die/mold under controlled temperature and pressure conditions to form an unvulcanized sleeve with teeth and troughs complementary to the projections/recesses on the shaping die/mold.
On the back surface of the unvulcanized sleeve, consisting of the cloth and rubber layers, discrete holes tend to generate. That is, as the rubber layer is forced into the recesses, the rubber at the teeth tends to fold inwardly to create discrete gaps or indentations, hereinafter referred to as “discrete holes”. As subsequent components are built up upon the shaping die/mold, the discrete holes become fully surrounded and ultimately remain intact on the completed belt. These discrete holes serve as locations at which cracks are prone to being generated as the belt is operated.
One solution, that eliminates these discrete holes, is disclosed in JP 2005-54851 A. In this document, it is described that the discrete holes can be eliminated by cutting, grinding, or polishing the rubber layer at the surface having the discrete holes, to thereby eliminate the same preparatory to applying the next layer. Thereafter, the layers, such as a cushion rubber layer, load carrying member/cord, separate rubber sheet/layer defining the tension section, etc., are successively wrapped to complete a sleeve preform preparatory to vulcanization. While the cutting, grinding, and/or polishing processes may effectively eliminate the discrete holes, these processes generally generate a significant amount of scrap in the form of cutting chips, grinding chips, or polishing chips. For convenience, and environmental purposes, it is desirable to avoid the generation of this type of scrap.